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Entomologists Amazed By How Dragonflies Dance
 
 
by News Staff - sci-news.com
Dragonflies move like ballet dancers when they hunt, according to new research by entomologists from the University of Arizona, Howard Hughes Medical Institute, and Union College in Schenectady, NY.
The Blue dasher, female, photographed in Skaneateles, NY. Image credit: R.A. Nonenmacher / CC BY-SA 3.0.


"Dragonflies on the hunt perform internal calculations every bit as complex as those of a ballet dancer," said Dr Anthony Leonardo of Howard Hughes Medical Institute, who is the senior author of a paper published in the journal Nature.

Dr Leonardo and his collaborators spent several years devising a system that allows them to track a dragonfly's body movements as it intercepts its prey.

Their approach is based on the same technology used to translate the movements of actors into computer animation. Using the position of each flash of light, the team can reconstruct an outline of the dragonfly as it flies.

Common Whitetail - Adult Male
Common Whitetail - Adult Female

The scientists filmed the movements of common whitetails (Plathemis lydia) as they chased after either a fruit fly or an artificial prey – a bead maneuvered by a pulley system – whose movements they could precisely control. They focused on following the orientation of the dragonfly's head and body.

When the researchers analyzed their videos, it was clear that the dragonflies were not simply responding to the movements of the prey.

Instead, they made structured turns that adjusted the orientation of their bodies – even when their prey's trajectory did not change.

"Those turns were driven by the dragonfly's internal representation of its body and the knowledge that it has to rotate its body and line it up to the prey's flight path in a particular way," Dr Leonardo said.

Dragonflies always aligned themselves so that they would intercept their prey from below, reducing the risk of detection.

"At the end of the chase, the fly makes a basket out its legs and the prey drops into it," Dr Leonardo said.

Those shifts in orientation create a challenge for the predator.

The scientists found that each dragonfly moved its head to keep the image of its prey centered on the eye, despite the rotation of its own body.

The head movements happened too fast to be a reaction to visual disturbances created by the rotation of the dragonfly's body. Instead, the head movements must be planned based on the insect's predictions about how to stabilize the image of its prey.

"The movements we observed are so fine-tuned that they keep the image of the prey fixed in the crosshairs of the dragonfly's eyes – their area of greatest acuity – during the duration of the chase. That allows the dragonfly to receive two channels of information about its prey," Dr Leonardo said.

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